[PATCH] tpm: Use kfree_sensitive() to free auth session in tpm_dev_release()

[Gunnar Kudrjavets <gunnarku@amazon.com>]

tpm_dev_release() uses plain kfree() to free chip->auth, which contains
sensitive cryptographic material including HMAC session keys, nonces,
and passphrase data (struct tpm2_auth).

Every other code path that frees this structure uses kfree_sensitive()
to zero the memory before releasing it: both tpm2_end_auth_session()
and tpm_buf_check_hmac_response() do so. The tpm_dev_release() path
is the only one that does not, leaving key material in freed slab
memory until it is eventually overwritten.

Use kfree_sensitive() for consistency with the rest of the driver and
to ensure session keys are scrubbed during device teardown.

Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
Signed-off-by: Gunnar Kudrjavets <gunnarku@amazon.com>
Reviewed-by: Justinien Bouron <jbouron@amazon.com>
---
 drivers/char/tpm/tpm-chip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 082b910ddf0d..17d9d71774ec 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -247,7 +247,7 @@ static void tpm_dev_release(struct device *dev)
 	kfree(chip->work_space.context_buf);
 	kfree(chip->work_space.session_buf);
 #ifdef CONFIG_TCG_TPM2_HMAC
-	kfree(chip->auth);
+	kfree_sensitive(chip->auth);
 #endif
 	kfree(chip);
 }

base-commit: 03e5553f5fb99cb47c315e167a604a9c69e6f724
-- 
2.47.3